settings对象

通常要获取settings的配置项时候都会通过from django.conf import settings获取。

settings是一个LazySettings实例对象，在django.conf的__init__.py下settings = LazySettings()，由于模块本身只执行一次所以这是一个单例（简单说就是你每次导入的settings都是同一个实例对象）

参考：

class LazySettings(LazyObject)

class LazySettings(LazyObject):    def _setup(self, name=None):        # 根据配置的settings文件导入配置        settings_module = os.environ.get(ENVIRONMENT_VARIABLE)        pass        self._wrapped = Settings(settings_module)     # 和下面的UserSettingsHolder一样都是BaseSettings子类    def __getattr__(self, name):        # 获取属性时候没有导入配置则导入        if self._wrapped is empty:            self._setup(name)        return getattr(self._wrapped, name)    def configure(self, default_settings=global_settings, **options):        # 手动自定义配置，没有配置才能使用        if self._wrapped is not empty:            raise RuntimeError('Settings already configured.')        holder = UserSettingsHolder(default_settings)    # 和上面的Settings一样都是BaseSettings子类        for name, value in options.items():            setattr(holder, name, value)        self._wrapped = holder                @property    def configured(self):        return self._wrapped is not empty

父类LazyObject中很多类似__getattr__ = new_method_proxy(getattr)的使用，没有配置时候先导入配置 ，然后获取self._wrapped配置中的信息和属性

相当于：__getattr__ = getattr(self,_wrapped, *args)

def new_method_proxy(func):    def inner(self, *args):        if self._wrapped is empty:            self._setup()        return func(self._wrapped, *args)    return inner

测试

In [7]: dir(settings)Out[7]:['ABSOLUTE_URL_OVERRIDES', 'ADMINS', 'ALLOWED_HOSTS', 'ALLOWED_INCLUDE_ROOTS',# 省略...

总结：LazySettings主要用于控制配置文件的来源

class Settings

实际上配置文件的配置都在Settings中, 配置文件中的配置（必须全部大写）都添加为Settings实例的属性。UserSettingsHolder中配置都在LazySettings中手动循环添加，这里不在赘述，下面只看Settings导入配置过程

class BaseSettings(object):    """    Common logic for settings whether set by a module or by the user.    """    def __setattr__(self, name, value):        # "MEDIA_URL", "STATIC_URL"两项配置必须以"/"结尾        if name in ("MEDIA_URL", "STATIC_URL") and value and not value.endswith('/'):            raise ImproperlyConfigured("If set, %s must end with a slash" % name)        object.__setattr__(self, name, value)

class Settings(BaseSettings):    def __init__(self, settings_module):        # 配置项必须为全大写        for setting in dir(global_settings):    # 导入默认配置文件的配置，即初始化配置            if setting.isupper():                setattr(self, setting, getattr(global_settings, setting))        # store the settings module in case someone later cares        self.SETTINGS_MODULE = settings_module        mod = importlib.import_module(self.SETTINGS_MODULE)        # import指定的配置文件        self._explicit_settings = set()        for setting in dir(mod):        # 导入配置指定配置文件中的配置项覆盖默认配置            if setting.isupper():                setting_value = getattr(mod, setting)                pass                setattr(self, setting, setting_value)                self._explicit_settings.add(setting)            pass        def is_overridden(self, setting):        return setting in self._explicit_settings

现在settings中已经有所有的配置项

conf包

|- conf|--- app_template            # app目录模板：manage.py startapp|--- locale                        # 语言包和对应时间表示格式|--- project_template        # app项目模板 ：manage.py startproject|--- urls